The Cambridge Natural History, Vol. 08 (of 10)

CHAPTER XIII

SAURIA (CONTINUED)—OPHIDIA—SNAKES 581

INDEX 651

{xi}SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK

CLASS AMPHIBIA.

Sub-Class. Order. Sub-Order. Family. Sub-Family.

STEGOCEPHALI (p. 78) STEGOCEPHALI LEPOSPONDYLI (p. 80) BRANCHIOSAURI (p. 80). AISTOPODES (p. 81). STEGOCEPHALI TEMNOSPONDYLI (p. 81) STEGOCEPHALI TEREOSPONDYLI (p. 83)

LISSAMPHIBIA (p. 84) APODA (p. 84) COECILIIDAE (p.89). URODELA (p. 94) AMPHIUMIDAE (p. 97). SALAMANDRIDAE (p. 102) Desmognathinae (p. 102). Plethodontinae (p. 103). Amblystomatinae (p. 109). Salamandrinae (p. 115). PROTEIDAE (p. 132). SIRENIDAE (p. 136). ANURA (p. 138) AGLOSSA (p. 143). PHANEROGLOSSA (p. 152) DISCOGLOSSIDAE (p. 152). PELOBATIDAE (p. 160). BUFONIDAE (p. 166). HYLIDAE (p. 185) Amphignathodontinae (p. 188). Hylinae (p. 189). CYSTIGNATHIDAE (p. 209) Hemiphractinae (p. 210). Cystignathinae (p. 211). Dendrophryniscinae (p. 224). ENGYSTOMATIDAE (p. 225) Engystomatinae (p. 225). Dyscophinae (p. 235). Genyophryninae (p. 236). RANIDAE (p. 237) Ceratobatrachinae (p. 237). Raninae (p. 238). Dendrobatinae (p. 272).

CLASS REPTILIA (p. 277).

PROREPTILIA (p. 285). Eryops (p. 286). Cricotus (p. 287).

Sub-Class. Order. Sub-Order. Family. Sub-Family.

PROSAURIA (p. 288) MICROSAURI (p. 288). PROSAURI (p. 290). PROTOROSAURI (p. 290). RHYNCHOCEPHALI (p. 292).

THEROMORPHA (p. 300) PAREIASAURI (p. 304). THERIODONTIA (p. 306). ANOMODONTIA (p. 309). PLACODONTIA (p. 311).

CHELONIA (p. 312) ATHECA (p. 333) SPHARGIDAE (p. 333). THECOPHORA (p. 338) CRYPTODIRA (p. 338) CHELYDRIDAE (p. 338). DERMATEMYDIDAE (p. 341). CINOSTERNIDAE (p. 342). PLATYSTERNIDAE (p. 345). TESTUDINIDAE (p. 345). CHELONIDAE (p. 378). PLEURODIRA (p. 388) PELOMEDUSIDAE (p. 390). CHELYDIDAE (p. 399). CARETTOCHELYDIDAE (p. 404). TRIONYCHOIDEA (p. 404) TRIONYCHIDAE (p. 404).

DINOSAURIA (p. 412) SAUROPODA (p. 418). THEROPODA (p. 420). ORTHOPODA (p. 424) STEGOSAURI (p. 425). ORNITHOPODA (p. 426) CERATOPSIA (p. 430).

CROCODILIA (p. 431) PSEUDOSUCHIA (p. 432). PARASUCHIA (p. 433). EUSUCHIA (p. 434) TELEOSAURIDAE (p. 450). METRIORHYNCHIDAE (p. 451). MACRORHYNCHIDAE (p. 451). GAVIALIDAE (p. 451). ATOPOSAURIDAE (p. 453). GONIOPHOLIDAE (p. 453). CROCODILIDAE (p. 454).

PLESIOSAURIA (p. 473) NOTHOSAURI (p. 476) MESOSAURIDAE (p. 476). NOTHOSAURIDAE (p. 477). PLESIOSAURI (p. 477) PLIOSAURIDAE (p. 477). PLESIOSAURIDAE (p. 478). ELASMOSAURIDAE (p. 478).

ICHTHYOSAURIA (p. 478) ICHTHYOSAURI (p. 483).

PTEROSAURIA (p. 484) PTEROSAURI (p. 486) PTERODACTYLI (p. 486). PTERANODONTES (p. 487).

PYTHONOMORPHA (p. 487) DOLICHOSAURI (p. 489). MOSASAURI (p. 489).

SAURIA (p. 491) LACERTILIA (p. 491) GECKONES (p. 502) GECKONIDAE (p. 507) Geckoninae (p. 507). Eublepharinae (p. 512). Uroplatinae (p. 512). LACERTAE (p. 513) AGAMIDAE (p. 515). IGUANIDAE (p. 528). XENOSAURIDAE (p. 536). ZONURIDAE (p. 536). ANGUIDAE (p. 537). HELODERMATIDAE (p. 540). LANTHANOTIDAE (p. 541). VARANIDAE (p. 542). XANTUSIIDAE (p. 547). TEJIDAE (p. 547). LACERTIDAE (p. 549). GERRHOSAURIDAE (p. 559). SCINCIDAE (p. 559). ANELYTROPIDAE (p. 564). DIBAMIDAE (p. 564). ANIELLIDAE (p. 564). AMPHISBAENIDAE (p. 565). PYGOPODIDAE (p. 567). CHAMAELEONTES (p. 567) CHAMAELEONTIDAE (p. 573).

OPHIDIA (p. 581) TYPHLOPIDAE (p. 593). GLAUCONIIDAE (p. 594). ILYSIIDAE (p. 594). UROPELTIDAE (p. 595). BOIDAE (p. 596) Pythoninae (p. 598). Boinae (p. 601). XENOPELTIDAE (p. 605). COLUBRIDAE (p. 606) Aglypha (p. 606) Acrochordinae (p. 606). Colubrinae (p. 607). Rhachiodontinae (p. 622). COLUBRIDAE Opisthoglypha (p. 623) Dipsadomorphinae (p. 623). Elachistodontinae (p. 625). Homalopsinae (p. 625). COLUBRIDAE Proteroglypha (p. 625) Elapinae (p. 626). Hydrophinae (p. 635). AMBLYCEPHALIDAE (p. 637). VIPERIDAE (p. 637) Viperinae (p. 638). Crotalinae (p. 644).

PART I. Amphibia

AMPHIBIA

"'s scheint, dass die hier oben keine Ahnung haben von dem Sumpf und Seiner Pracht." The "plattgedrückte Kröte," SCHEFFEL'S Trompeter von Säkkingen.

{3}CHAPTER I

AMPHIBIA

CHARACTERS AND DEFINITION–POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA–HISTORICAL ACCOUNT OF THE CLASSIFICATION OF AMPHIBIA

A bird is known by its feathers, a Beast by its hairs, a Fish by its fins, but there is no such obvious feature which characterises the Amphibia and the Reptiles. In fact, they are neither fish, flesh, nor fowl. This ill-defined position is indicated by the want of vernacular names for these two classes, a deficiency which applies not only to the English language. All the creatures in question are backboned, creeping animals. Those which are covered with horny scales, and which from their birth breathe by lungs only, as Crocodiles, Tortoises, Lizards, and Snakes, are the Reptiles. The rest, for instance, Newts or Efts, Frogs and Toads, are the Amphibia. Their skin is mostly smooth and clammy and devoid of scales; the young are different from the adult in so far as they breathe by gills and live in the water, before they are transformed into entirely lung-breathing, terrestrial creatures. But there are many exceptions. Proteus and Siren the mud-eel, always retain their gills; while not a few frogs undergo their metamorphosis within the egg, and never breathe by gills. If we add the tropical limbless, burrowing Coecilians, and last, not least, the Labyrinthodonts and other fossil forms, the proper definition of the class Amphibia,–in other words, the reasons for grouping them together into one class, separated from the other backboned animals,–requires the examination of many other characters.

{4}So far as numbers of living species are concerned, the Amphibia are the least numerous of the Vertebrata. There are about 40 limbless, burrowing APODA; 100 URODELA or tailed two- or four-footed newts, and about 900 ANURA, or tailless, four-footed frogs and toads; in all some 1000 different species. Few, indeed, in comparison with the 2700 Mammals, 3500 Reptiles, nearly 8000 Fishes, and almost 10,000 Birds. But we shall see that the Amphibia have not only "had their day," having flourished in bygone ages when they divided the world, so far as Vertebrata were concerned, between themselves and the Fishes, but that they never attained a dominant position. Intermediate between the aquatic Fishes and the gradually rising terrestrial Reptiles they had to fight, so to speak, with a double front during the struggle of evolution, until by now most of them have become extinct. The rest persist literally in nooks and corners of the teeming world, and only the Frogs and Toads, the more recent branch of the Amphibian tree, have spread over the whole globe, exhibiting almost endless variations of the same narrow, much specialised plan. The greatest charm of the Anura lies in their marvellous adaptation to prevailing circumstances; and the nursing habits of some kinds read almost like fairy-tales.

CHARACTERS OF THE AMPHIBIA.

1. The vertebrae are (a) acentrous, (b) pseudocentrous, or (c) notocentrous.

2. The skull articulates with the atlas by two condyles which are formed by the lateral occipitals. For exceptions see p. 78.

3. There is an auditory columellar apparatus, fitting into the fenestra ovalis.

4. The limbs are of the tetrapodous, pentadactyle type.

5. The red blood-corpuscles are nucleated, biconvex, and oval.

6. The heart is (a) divided into two atria and one ventricle, and (b) it has a conus provided with valves.

7. The aortic arches are strictly symmetrical.

8. Gills are present at least during some early stages of development.

9. The kidneys are provided with persistent nephrostomes.

10. Lateral sense-organs are present at least during the larval stage.

11. The vagus is the last cranial nerve.

12. The median fins, where present, are not supported by spinal skeletal rays.

13. Sternal ribs and a costal or true sternum are absent.

14. There is no paired or unpaired medio-ventral, copulatory apparatus.

15. Development takes place without amnion and allantois.

None of these characters is absolutely diagnostic, except 1 (c), and this applies only to the Anura and most of the Stegocephali.

{5}Numbers 1 (b), 1 (c), 2, 3, 4 and 12 separate the Amphibia from the Fishes.

Numbers 1, 6 (b), 7, 8, 9, 11, 13, 15 separate them from the Reptiles, Birds, and Mammals.

Number 2 separates them from the Fishes, Reptiles, and Birds.

Number 5 separates them from the Mammals.

Number 6 (a) separates them from the Fishes (excl. Dipnoi), Birds and Mammals.

We can, therefore, very easily define all the Amphibia, both recent and extinct, by a combination of the characters enumerated above. For instance, by the combination of numbers 2, 3 or 4 with either 7, 8, 9, 11, 13 or 15.

Amphicondylous Anamnia would be an absolutely correct and all-sufficient diagnosis, but it would be of little use in the determination of adult specimens; and the tetrapodous character is of no avail for Apoda. Amphicondylous animals without an intracranial hypoglossal nerve is a more practical diagnosis.

In the case of living Urodela and Anura the absence of any scales in the skin affords a more popular character; it is unfortunately not applicable to the Apoda, many of which possess dermal scales, although these are hidden in the imbricating transverse rings of the epidermis; and the frequent occurrence of typical scales of both ecto- and meso-dermal composition in many of the Stegocephali forces us to discard the scales, or rather their absence, as a diagnostic character of the class Amphibia. The same applies to the mostly soft, moist, or clammy, and very glandular nature of the skin.

THE POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA.–There is no doubt that the Amphibia have sprung from fish-like ancestors, and that they in turn have given rise to the Reptilia. The Amphibia consequently hold a very important intermediate position. It was perhaps not a fortunate innovation when Huxley brigaded them with the Fishes as Ichthyopsida, thereby separating them more from the Sauropsida (= Reptilia and Aves), than is justifiable,–perhaps more than he himself intended. The connecting-link, in any case, is formed by the Stegocephali; all the recent Orders, the Apoda, Urodela, and Anura, are far too specialised to have any claims to the direct ancestral connections. The line leading from Stegocephali to fossil Reptiles, notably to such Proreptilia as Eryops and Cricotus, and even to the Lepospondylous Prosauria, is extremely gradual, and the steps are almost imperceptible. Naturally, {6}assuming evolution to be true, there must have lived countless creatures which were a "rudis indigestaque moles," neither Amphibia nor Reptilia, in the present intensified sense of the systematist. The same consideration applies equally to the line which leads downwards to the Fishes. But the great gulf within the Vertebrata lies between Fishes and Amphibia, between absolutely aquatic creatures with internal gills and "fins," and terrestrial, tetrapodous creatures, with lungs and fingers and toes. On the side of the fishes only the Dipnoi and the Crossopterygii come into consideration.

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